Click on the image to watch a video clip about the challenges engineers faced when designing Citigroup Center Skyscraper in New York City.
Structure
Human dwellings and office buildings are not usually mass structures made by hollowing out piles of building materials. Frame structures, like the body of most buildings, have a skeleton of very strong materials, which supports the weight of the roof and covering materials. Most of the inside of the building is empty space. Extra walls can be built to separate different rooms, but they do not need to be particularly strong because the load-bearing framework supports the structure and everything in it.
Without these Load Bearing Walls the building would fall down.
Some objects, such as ladders, snowshoes, and spider webs, consist of only a frame. More complex objects may have other parts added to the frame, such as the pedals, gears, and brakes of a bicycle. The frame may be hidden beneath covering materials (as in umbrellas, automobiles, and boats) or left exposed (as in drilling rigs and steel bridges). Frame structures are relatively easy to design and build, making them one of the least expensive construction choices. Whether simple or complex, hidden or exposed, all frames must overcome similar problems. Do you remember building frame structures in other science classes? How did you fasten the parts together? How did you make your frames strong without using too much material? How did you shape or brace them so that they would not bend or collapse?
Certain kinds of frame structures present special design challenges. Tents and other lightweight structures need some type of anchor to fasten them securely to the ground. Very tall frame structures, such as communications towers, can easily become unstable unless they are carefully braced. Large, complicated projects, such as buildings and bridges, have many parts that all have to fit together perfectly when they are finally assembled at the building site. This can happen only if every detail of the design is calculated in advance.
Function
What is this thing supposed to do? The answer to this question will guide all of your design decisions. Simple? Not really. Most structures have several functions. Think of a bridge. Its job is to support … what?
Vehicles and people, of course, but the steel and concrete the bridge is made from can weigh many times more than the cars and trucks travelling across the bridge. Thus one very important function of any structure is to support its own weight.
Structures do more than just support loads. For example, a running shoe grips the ground or gym floor and cushions your foot bones from the impact of running. But it has many other functions, too. Designers have a hard time creating structures that perform all of their functions equally well. Plastic-covered running shoes certainly keep water out when you run through a puddle. But they also keep perspiration, moisture, in, so your feet soon get hot and sweaty. Most runners have shoes made with rubber and plastic soles and cloth uppers. This compromise does not let much puddle water in but does let most perspiration out.
How well must a structure perform its functions? Designers work to a set of specifications that give precise, measurable standards their structure must meet. Specifications for a running shoe might be
• sole must flex 100, 000 times without cracking
• materials must not contain chemicals that could irritate the skin
Aesthetics One very important design specification is seldom written down. The best designs look good. Designers refer to such designs as “aesthetically pleasing.” (Aesthetics is the study of beauty in art and nature.)
Think of an attractive car, building, or butterfly. It might feature shapes that are repeated or carefully arranged. There might be interesting textures and colors that are carefully chosen to be harmonious, look nice together, or contrasting (the objects' differences make it look beautiful). Sometimes the choice of materials and the methods used to make a structure can have a huge impact on aesthetics. The marble columns used in classically designed Greek buildings are beautiful, functional, strong … and expensive! The concrete columns under a highway overpass are functional, strong, and relatively inexpensive. Check with your art teacher for other principles of design that can help your projects look attractive.
Above all, architects and engineers try to keep their designs simple. Clean designs look better than over-complicated, busy ones. So remember to keep it simple!
This bridge uses columns for support.
Take a close look at the columns used to design this Ancient Greek Temple.